Field of the Invention
The present invention relates to a fabrication apparatus having a deposition apparatus for use in deposition of materials allowed to be deposited by evaporation (hereafter, they are called evaporation materials). Particularly, the invention is an effective technique when organic materials are used as the evaporation materials.
Description of the Related Art
In recent years, the research of light emitting devices having EL elements as self-luminous elements has been conducted actively. In particular, a light emitting device using organic materials as EL materials is receiving attention. The light emitting device is also called an organic EL display or an organic light emitting diode.
In addition, the EL element has an anode, a cathode, and a layer containing organic compounds where an electric field is applied to obtain electroluminescence (hereafter, it is denoted by EL layer). Electroluminescence in the organic compounds has light emission (fluorescence) in returning from the singlet excited state to the ground state, and light emission (phosphorescence) in returning from the triplet excited state to the ground state. The light emitting devices fabricated by the deposition apparatus and a deposition method of the invention can be adapted to in either case of light emission.
As different from liquid crystal display devices, the light emitting devices have characteristics in that they have no problem about the viewing angle because they are a self-luminous type. More specifically, they are more suitable as displays used in outdoors than the liquid crystal displays. Various forms for use have been proposed.
The EL element has a structure in which the EL layer is sandwiched between a pair of electrodes. The EL layer generally has a multilayer structure. Typically, the multilayer structure of anode/hole transport layer/emissive layer/electron transport layer/cathode is named, which was proposed by Tang, Eastman Kodak Company. This structure has significantly high luminous efficiency, which is adopted for most of light emitting devices now under research and development.
Furthermore, other than this, these structures are fine to be layered over the anode in these orders: the structure of hole injection layer/hole transport layer/light emitting layer/electron transport layer, and alternatively the structure of hole injection layer/hole transport layer/light emitting layer/electron transport layer/electron injection layer. Moreover, it is acceptable to dope fluorescent dyes to the light emitting layer. Besides, it is fine that these layers are all formed of low weight molecular materials or all formed of polymeric materials.
In this specification, the entire layers disposed between the anode and the cathode are collectively called the EL layer. Accordingly, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, and the electron injection layer are all considered to be included in the EL layer.
In the specification, the light emitting element formed of the anode, the EL layer, and the cathode is called the EL element. The EL element has two systems: the system in which the EL layer is formed between two kinds of stripe electrodes disposed orthogonal to each other (simple matrix system), and the system in which the EL layer is formed between an opposite electrode and pixel electrodes connected to TFTs and arranged in matrix (active matrix system).
The EL materials forming the EL layer are generally classified into low weight molecular (monomer based) materials and polymeric (polymer based) materials. The low weight molecular materials are mainly deposited by evaporation.
The EL materials tend to be deteriorated extremely, which are easily oxidized and deteriorated by the existence of oxygen or moisture. On this account, photolithography processes cannot be performed after deposition. For patterning, deposition and separation need to be conducted simultaneously with a mask having opening parts (hereafter, it is called a mask). Therefore, almost all the sublimed organic EL materials have been deposited over the inner wall of a film-formation chamber or a wall-deposition shield (a protection plate for preventing the evaporation materials from being deposited over the inner wall of the film-formation chamber).
In a traditional evaporation apparatus, the space between a substrate and an evaporation source has been set wider in order to improve the uniformity of the film thickness, which has caused the apparatus itself to be large-sized. Moreover, because of the wide space between the substrate and the evaporation source, the deposition rate becomes slow, the time required to exhaust the inside of the film-formation chamber takes long time, and throughput drops.
In addition, in the traditional evaporation apparatus, the utilization efficiency for expensive EL materials is about one percent or below, which is extremely low to cause the fabrication costs of the light emitting device to be extremely high.